Recording sheet

ABSTRACT

A recording sheet comprising a support having coated thereon a layer of a color developer which is capable of forming a distinct color when contacted with a color former. The color developer contains a combination of (i) a polymer of an aromatic carboxylic acid having at least one hydroxyl group with an aldehyde or acetylene and (ii) a metallic compound.

United States Patent 1 Hayashi et al. 1

1111 3,767,449 [451 Oct. 23, 1973 RECORDING SHEET [75] Inventors: Takao Hayashi; Hajime Kato; Akio Miyamoto, all of Saitama, Japan [73] Assignee: Fuji Photo Film Co., Ltd.,

, Kanagawa, Japan [22] Filed: Sept. 28', 1971 [21] Appl. No.: 184,608

[30] Foreign Application Priority Data Sept. 28, 1970 Japan 45/84539 Dec. 15, 1970 Japan.... 45/112039 [56] References Cited UNITED STATES PATENTS 3,540,914 11/1970 Lin l17/36.2 3,682,680 8/1972 Hayashi et a1. 117/36.2

Primary Examiner-Murray Katz AttorneyRichard C. Sughrue et al.

[57] ABSTRACT A recording sheet comprising a support having coated thereon a layer of a color developer which is capable of forming a distinct color when contacted with a color former. The color developer contains a combination of (i) a polymer of an aromatic carboxylic acid having at least one hydroxyl group with an aldehyde or acetylene and (ii) a metallic compound.

15 Claims, No Drawings v RECORDING SHEET BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording sheet and a color developer therefor and more particularly to a recording sheet having coated'thereon a novel color developer layer and a novel color developer for the recording sheet. r

,2. Description of the Prior Art There have been known recording sheets utilizing a color reaction of a colorless organic compound (hereinafter referred to as -a fcoloriforrner") and an adsorbent material capable of forming a distinct color when contacted with the color'former.

Examples of recording sheets using this phenomenon are pressure-sensitive recording sheets suchas in U.S-. Pat. Nos. 2,505,470, 2,505,489, 2,550,471, 2,548,366, 2,712,507, 2,730,456, 2,730,457 and 3,418,250 and well-knownheat-sensitive recording sheets. Further, a printing method. is'k'nown where an ink, containing-the color former, is applied to the color developer sheet through amedium such as a stencil.

In all cases, the above phenomenon of the color-reaction between the color former and the color developer is utilized under pressure with a pen' or stylus, under heat,'etc.

The color former may be dissolved in a solvent such as chlorinated diphenyl, chlorinated paraffin or other organic solvent. The solution may be dispersed in a binder and/or may be microencapsulated, and then coated onto a support such as-paper, plastic film, resincoated paper, etc.

with a binder such as a styrene-butadiene rubber latex and then coated'on or impregnated into a base support before or directly before recording.

The color former and color developer may be coated onto the same surface or opposite surfaces of a support, or the different supports.

Usually, after the color developer is coated onto the support, a desensitizer is locally coated thereon in order that unnecessary color formation be prevented in certain portions of the surface as shown in US. Pat. No. 2,777,780. Another embodiment for the prevention of color formation is to locally coat the color de, veloper on the support or the coated layer of the color former without using the desensitizer.

As'the above described color developer, there are clays such as acid clay, active clay, atapulgite, zeolite, bentonite, etc., phenol resins (U.S. Pat. Nos. 3,516,845, 3,540,91 l) and organic compounds such as succinic acid, tannic acid, gallic acid or phenol compounds (U.S. Pat. No. 3,244,548) are known. Such organic compounds are not practically employed for the reason that the color developing ability of the color developer sheet which is a support having coated thereon Further, in cases where the above color developer is locally coated onto a support to form a color developer sheet, if large amount thereof (7-10 3 per l m of the support) is coated, the color developer sheet cannot form sufficient color when contacted with the color former. As a result, the local coating method is limited.

SUMMARY OF THE INVENTION The inventors have found that all defects of the color developer sheet and ink using the above described organic compounds can be completely removed by combining a polymer of an aromatic carboxylic acid having at least one hydroxyl group or its anhydride and aldehyde or acetylene with a metallic compound. That is, the inventors have found'that a color developer composed of a polymer of an aromatic carboxylic acid having at least onehydroxyl group or its anhydride with an aldehyde or acetylene and a metallic compound is far stronger in color developing ability than only a polymer of an aromatic carboxylic acid having at least one bydroxyl group with aldehyde or acetylene or its anhydride, or only a metallic compound, and that the color formed or the color former sheet is stronger in light resistance.

I DESCRIPTION OF THE PREFERRED I EMBODIMENTS As the examples of polymers of an aromatic carboxylic acid with aldehyde or acetylene, there are salicylic acid-aldehyde polymers, p-hydroxybenzoic acidaldehyde polymers, 2,6-dihydroxybenzoic acidaldehyde polymers, salicylic acid-acetylene polymers and the like.

While well-known color developers such as phenolaldehyde polymers,phenol-acetylenepolymers, maleic acid-rosin polymers, partially-or all hydrolyzed styrenemaleicanhydride polymers, etc., do not give excellent color developing ability even if they are used with a metallic compound, the color developing ability according to the present invention is more increased.

Accordingly, one feature of the present invention is to use a polymer of aromatic carboxylic acid having at least one hydroxyl group with an aldehyde or an acetylene.

As a metallic compound used in the present invention, there are metallic oxides, metallic hydroxides and metallic carbonates, etc. As a metallic oxide, an oxide of a metal belonging to group Ila of the Periodic Table, such as magnesium oxide, calcium oxide, barium oxide, etc., an oxide of a metal belonging to group llb of the Periodic Table, such as zinc oxide, cadmium oxide, mercury oxide, etc., an oxide of a metal belonging to group Illa of the Periodic Table, such as aluminum oxide, etc., and an oxide of a metal belonging to group lVa of the Periodic Table, such as tin oxide, lead oxide, etc., are particularly effective.

As a metallic hydroxide, a hydroxide of a metal belonging to group Ila of the Periodic Table, such as magnesium hydroxide, calcium hydroxide, etc., a hydroxide of a metal belonging to group llb of the Periodic Table, such as zinc hydroxide, cadmium hydroxide, mercury hydroxide, etc., a hydroxide of a metal belonging to group lIIa of the Periodic Table, such as aluminum hydroxide, etc., and a hydroxide of a metal belonging to group IVa of the Periodic Table, such as tin hydroxide, lead hydroxide, etc., are particularly effective.

As a metallic carbonate, a carbonate of metal belonging to group lla of the Periodic Table, such as magnesium carbonate, calcium carbonate, etc., a carbonate of metal belonging to group Ilb of the Periodic Table, such as zinc carbonate, cadmium carbonate, etc., and a carbonate of metal belonging to group IVa of the Periodic Table, such as lead carbonate, etc., are particularly effective.

In addition, basic aluminum acetate, basic lead acetate, basic lead hydroxide, basic magnesium carbonate, basic lead carbonate, etc., are effective.

Among the metallic compounds, zinc oxide, cadmium oxide, magnesium oxide, zinc hydroxide, magnesium hydroxide, calcium hydroxide, zinc hydroxide, magnesium hydroxide, calcium hydroxide, zinc carbonate, calcium carbonate, magnesium carbonate, etc., are particularly effective for an aromatic carboxylic acid having at least one hydroxyl group. More particularly, oxides or carbonates of zinc are effective. The metallic compound may be crushed and converted in size so as to pass a sieve of more than 325 mesh.

The ratio of the metallic compound and the polymer is more than one part by weight of the polymer, preferably -30 parts by weight based on 100 parts by weight of metallic compound, desirably 2-100 parts by weight. Furthermore, for the purposes of increasing color developing ability and light resistance, a pigment may be added to the color developer. The pigment contains aluminum silicate, zinc silicate, lead silicate, tin silicate, colloidal hydrated aluminum silicate, zeolite, bentonite, laolinite, active clay, acid clay, talc and the like.

The amount of pigment does not have a critical value. For example, more than one part by weight, preferably 10-500 parts by weight per 100 parts by weight of the polymer can be employed.

The color developer of the invention can be prepared by dissolving or dispersing the polymer and the metallic compound in water or in an organic solvent such as methanol, ethanol, butanol, ethyl acetate, butyl acetate, benzene, toluene, acetone, tetrahydrofuran or methylene chloride. Water and the organic solvent may be mixed. Preferably the solvent is capable of dissolving the polymer. In case of adding the pigment, it may be dispersed in water, in the organic solvent, in the solution or in the dispersion.

The thus-prepared solution or dispersion can be coated onto a support, if necessary, together with a binder such as gum arabic, ethyl cellulose, styrenebutadiene copolymer, nitrocellulose, styrene-butadiene latex, methylmethacrylate-butadiene latex, etc.

It should be noted that the'coated layer of color developer can be maintained on the support even if the binder is not present in the layer.

The amount of the color developer coating composition is not specifically limited to obtain sufficient color. For example, it is more than 0.1 g/m"', preferably 0.5-10 g/m. The upper limit of coating amount is not limited from the point of view of color developing activity, and the above range is only due to economic reasons.

The color developer composition can be coated onto a support by all kinds of coating methods, because the present invention is basically characterized by using the polymer and the metallic compound. For example, the metallic compound and, if necessary, the pigment may be coated onto the support with the binder, and then the dissolved or dispersed polymer may be coated thereon.

As another embodiment for preparing a color developer composition, the binder is dissolved in the organic solvent and a plasticizer is added and then both the polymer and the metallic compound are dissolved or dispersed in the resulting solution.

The plasticizer may contain esters of phosphoric acid, phthalic acid, adipic acid or sebacic acid (e.g., tributyl phosphate, dibutyl phthalate, dioctyl phthalate, butyl adipate, dibutyl sebacate), hydrocarbon such as chlorinated paraffin, and glycerides of unsaturated fatty acids such as castor oil.

In this case, for the purpose of stabilizing the color developer composition which may be used as a coating ink, an alkali metal salt of an organic acid, or an alkali may be added to the composition. The alkali metal salt of an organic acid is, for example, a lithium salt, a sodium salt or a potassium salt of butylic acid, caprylic acid, palmitic acid, oleic acid, linoleic acid, linolenic acid, benzoic acid, and the like. The alkali may be, for example, sodium hydroxide, potassium hydroxide, sodium carbonate, sodium silicate, borax and conventional alkali compounds. The amount of the alkali is 0.01-1 part by weight per one part by weight of the polymer.

Each component may be dissolved or dispersed by means of ball mill or sand mill.

The thus-prepared color developer ink can be locally applied to a support.

A color developer sheet and the color developer of the invention can be used in combination with conventional color former such as crystal violet lactone, benzoyl leuco methylene blue, malachite green lactone, rhodamine B lactam, fluoranes (US. Pat. Nos. 3,501,331, 3,514,310, 3,514,311, 3,540,911), spiropyrans (US. Pat. No. 3,293,060), mixtures thereof, and the like.

The modification of the invention can be easily carried out by one skilled in the art in accordance with conventional information, techniques, and the like.

The color formers for pressure-sensitive copying paper are ordinarily employed in combination in order to secure the instantaneous color-forming property and light fastness of the colored image. For example, a combination of instantaneous color-forming crystal violet lactone as a primary color former and benzoyl leucomethylene blue having excellent light fastness has been most well known; however, the colored image obtained by contacting the combination of color formers with an aromatic carboxylic acid or its anhydride tends to disappear when it is allowed to stand in a room or is exposed to sunlight, since crystal violet fades before benzoyl leucomethylene blue is color formed. However, such a defect as described above is removed in the present invention, since, on the color developer sheet using an aromatic carboxylic acid or its anhydride and a metalliccompound in combination, crystal violet lactone is strong in light fastness and does not fade before the benzoyl leucomethylene blue is color formed.

tone

This will be clear from the light fastness of crystal violet lactone in the examples described below.

In comparison with the conventional clay-coated paper, the color developer sheet of the present invention has the following advantages: v

The conventional clay-coated paper tends to be decreased in sensitivity of clay, when being allowed to stand in air, because of adsorbing materials in air on the active point of the clay. That is, the color developing ability of the color developer sheet is remarkably lowered with time.

In the color developer sheet of the present invention, such defect has been improved. And, in case of manufacturing a color developer sheet in accordance with the present invention, sufficient color developing abil ity and other properties necessary to the color developer sheet for pressure-sensitive paper can be satisfied with smaller coating amounts than in the conventional clay paper. That is, the amount of color developer of the present invention to be coated is sufiicient with 0.1-4 g/m while in the conventional clay paper the amount to be coated is 7-10 g/m. Thus, it is possible to make the color developer sheet by a size spray coating by means of a machine because only a small amount is required and the physical properties of the liquid can be freely varied different from clay, which results in a remarkable effect not only on performance but also on production.

Although the color formed on the clay-coated paper is easily caused to disappear or to be lowered in density when wetted with water, the color formed on the color developer sheet of the present invention has such an excellent property that the color density is not lowered even in case of being wetted with water.

Furthermore, the color developer of the present invention can give the similar color developing ability with smaller amounts (about 2 g/m if a natural or synthetic high molecular weight substance or a waterrepellent material is previously coated on the surface of paper. v

' The present invention will be illustrated using a pressure-sensitive recording paper with the following examples.

The effect of the color developer sheet of the present invention was confirmed with the following color former sheet.

Microcapsules containing a color former were manufactured, for example, according to the specification of U. S. Pat. No. 2,800,457, as follows:

10 parts by weight of acid-treated pigskin gelatin and 10 parts by weight of gum arabic were dissolved in 400 parts by weight of water at 40 C and 0.2 part by weight of Turkey Red oil was added thereto as an emulsifier, and 40 parts by weight of color former oil were emulsified and dispersed therein. 3

The color former oil is 2 percent of crystal violet lac- 3-dibenzylamino-7-diethylaminofluorane dissolved in an oil consisting of 4 parts by weight of chlorinated diphenyl and one part by weight of kerosene. The emulsification was stopped when the size of the oil droplets became 5 microns on an average. Water at 40 C was added thereto to 900 parts by total weight and the stirring was continued. At this time attention must be paid so that the liquid temperature does not decrease to below 40 C. Next, 10 percent acetic acid was added thereto to adjust the pH of the system to 4.0 to 4.2 and to cause coacervation. The stirring was further continued and, after 20 minutes, the system was cooled with ice to gelate a coacervate film deposited around an oil droplet. When the liquid temperature became 20 C, 7 parts by weight of 37 percent formaldehyde were added thereto and at 10 C, a 15 percent aqueous solution of caustic soda was added to adjust the pH to 9. At this time, addition of caustic soda must be carried out with sufficient attention. The liquid temperature was raised to 50 C by heat under stirring for 20 minutes.

The microcapsules thus obtained were conditioned to 30 C and thereafter were coated onto a 40 g/m paper in 6 g/m as a solid content and dried. Also in case of other color formers, the recording paper was manufactured in the same manner as described above.

In the following examples, part means part by weight.

Example 1 138 parts of salicylic acid and 325 parts of 37 percent formaldehyde were polymerized by adding 250 parts of 12 N sulfuric acid as a catalyst thereto and heating at --97 C for l hour. After dissolving or dispersing 20 parts of the resulting polymer (P-l and 10 parts of one of the below described binders in 300 parts of one of the below described solvents, parts of one of the below described metallic compounds passing a sieve of 325 mesh were dispersed therein under stirring. The resulting coating was coated onto a 40 g/m paper so as to give a solid content of 5 g/m and dried.

On the other hand, following samples were prepared for comparison:

Comparative Example lb 20 parts of the polymer (P-l) polymerized by the method of Example 1 and 1.7 part of one of the below described binders were dissolved or dispersed in one of the below described solvents and the resulting coating was coated onto a 40 g/m paper in an amount of 0.78 g/m Comparative Example la I00 parts of one of the below described metallic salts passing a sieve of 325 mesh was dispersed in one of the below described solvents and, in addition, 8.3 parts of one of the below described binders was dissolved or dispersed therein. The resulting coating was coated onto a 40 g/m paper in a solid content of 4.2 g/m and dried.

Results of Comparative Test 1 l. The color developer sheets of Example 1, Comparative Examples la and lb were placed on a color former sheet (crystal violet lactone) and pressurized under 600 kg/cm to form color images. After allowing them to stand at dark for l hour, spectral absorption curves between 400 and '700 m in wavelength were measured and the color developing abilities of color developer sheet were observed as density (D at the maximumabsorption (wavelength 610 mu).

2. Color images were formed on the color developer sheets of Example 1, Comparative Examples la and lb by using the color former sheet (3-dibenzylamino-7- diethylaminofluorane) in the same manner as in the above Comparative Test 1.

After being allowed to stand at dark for 1 hour, the

spectral absorption curves between 400 and 700 m in wavelength were measured and the color developing abilities of color developer sheets were observed as density (D at the maximum absorpiton (wavelength 600 mu).

Comparative Example 2a 100 parts of one of the below described metallic salts passing a sieve of 325 mesh was dispersed in one of the The results of (l) and (2) are as shown in Table l. 5 below described solvents and, in addition, 7.7 parts of TABLE 1 Color density of Colordensity of 3-dibenzylamino crystal violet 7-diethyl- Class Polymer Metallic compound Solvent Binder lactone amino'fluorane Examplel p-l Zinc carbonate Ethanol Ethyl cellulose 0.962 0.893 Comparative example l-a. o d Example 1 p-l Zincpxide. Comparative example l-a ..do Example I Zinc hydrozide.. Comparative example I do Example 1 alcium carbonate Comparative example l-a.. ..do

Example I Comparative example la.. o Example 1 p-l Aluminum ..do ..do 0.590

hydroxide. Comparative example l-a ..do ..do ..do 0.293 Examplel p-l Magnesium ..do ..do 0.590 0.643

hydroxide. Comparative example l-a ..do ..do ..do 0.310 0.780 Comparative example l-b p-l. ..do ..do 0.225... 0.283 Example 1 p-l Zinc carbonate Ethanol 270 parts Ethyl cellulose 0.902 0.845

water 30 parts. Comparative example 1-a ..do ..do ..do not color not color. Comparative example l-b p-l. ...do.. ..do 0.203 0.267. Examplel p-l. Zinc carbonate. Benzene Styrene-butadiene 0.975 0.9ll.

atex. Comparative example l-a ..do ..do ..do not color... not color. Comparative example l-b p-l ..do ..do 0.221 0.292.

Thus, the color developer sheet of the present invention was higher in color developing ability, and thev color image formed on the present color developer sheet was not lowered in color density even in the case of being wetted with water.

A similar effect was shown on other color formers.

Example 2 154 parts of 2,6-dihydroxybenzoic acid and 325 parts of 37 percent formaldehyde were polymerized by adding 250 parts of 12 N sulfuric acid as a catalyst thereto and heating at 95-97 C for 1 hour. After dissolving or dispersing 30 parts of the resulting polymer (P-2) and parts of one of the below described binders in 300 parts of one of the below described solvents, 100 parts of one of the below described metallic compounds passing a sieve of 325 mesh were dispersed therein under stirring. The resulting coating was coated onto a 40 g/m paper in a solid content of 5 g/m and dried.

On the other hand, the following samples were prepared for comparison:

Comparative Example 2b parts of the polymer (P-2) polymerized by the method of Example 2 and 23 parts of one of the below described binders were dissolved or dispersed in one of the below described solvents and the resulting coating was coated onto a 40 g/m paper in an amount of 1.2

one of the below described binders was dissolved or dispersed therein. The resulting coating was coated onto a 40 g/m paper in a solid content of 3.8 g/m and dried.

Results of Comparative Test 2 l The color developer sheets of Example 2, Comparative Examples 2a and 2b were placed on a color former sheet (crystal violet lactone) and pressurized under 600 kg/cm After being allowed to stand in the drak for 1 hour, the spectral absorption curves between 400 and 700 my. in wavelength were measured and the color developing abilities of color developer sheets were observed as density (D at the maximum absorpg/ The results of l) and (2) were as shown in Table 2.

TABLE 2 Color density of 3-dibenzylamino- Color density of 7-diethyl-aminocrystal violet fluorane (D Number Polymer Metallic compound Solvent Binder lactone (D Example 2 p-2 Zinc carbonate Ethanol... Ethyl cellulose... 0.982 0.933. Comparative example 2-a. o ..do.... .....do not color... not color. Example 2 p-2 Zinc oxide ..do ..do 0.850 0.815.

Comparative example 2-a Basic lead hydroxide...

....... Basic aluminum acetate.

Example 3 250 parts of 12 N sulfuric acid were added to 138 parts of salicylic acid and 325 parts of 37 percent formaldehyde and were heated and stirred at 95-97 C for l hour. After dissolving or dispersing 40 parts of the above prepared polymer (P-l) and parts of the below described binder in 300 ml of the below described solvent, 30 parts of the below described metallic compound passed through a sieve of 325 mesh and 30 parts of the below described inorganic pigment were added thereto while stirring. This coating liquid was coated onto a 40 g/m paper by means of a coating rod with a solid content of 4.5 g/m and dried.

Comparative Example 3 After dissolving or dispersing 40 parts of polymer polymerized by the method of Example 3 and 0.7 parts of the below described binder in 300 ml of the below described solvent, 30 parts of the below described metallic compound which passes through a sieve of 325 mesh were added thereto while stirring. This coating liquid was coated onto a 40 g/m paper by means of a coating rod in .a solid content of 3.5 g/m and dried.

Results of Comparative Test 3 Color developer sheets of Example 3 and Comparanot color.......... not color.

not color. 0.736. 0.230. 0.798.

sheet (crystal violet lactone or 3-dibenzylamino-7- I diethylaminofluorane) and pressurized under 600 15 tion was shown as the fresh density.

The r sylt a e shown tbst lqw ns Ta e Example 4' 250 parts of 12 N sulfuric acid were added to 154 parts of 2,6-dihydroxyl benzoic acid and 325 parts of 32 percent formaldehyde and heated and stirred at 95-97 C for 1 hour. Using the polymer polymerized by the publicly known method, a color developer sheet was obtained in the same manner as in Example 3.

Comparative Example 4 Using the polymer prepared by the method of Example 4, a color developer sheet for comparison was obtained in the same manner as in Comparative Example 3.

Results of Comparative Test 4 35 Using the color developer sheets of Example 4 and r mmp e c wa rlaq o th c r cvs qpsi Qqu xs.Examizlsfhlbssams test s in gmpara- T 5 15 Fresh density of E Fresh i using 3- density l dibenzyl- Example A of using amino-7- l and I crystal diethylcomparative violet amino No. exampleB l Polymer Metallic compound Inorganic pigment Solvent (300 ml) Binder lactone fluorane 1 A P-l Zinc oxide Zinc silicate Ethanol Ethyl cellulose 0.77 0.58 ..do... ..do o ..do .63 .53 2 do Zinc carbonate..... Organic Ethanolzwater ..do 1.03 .90

bentonite.. if L vo.raro.

do ..do ..do ..do 0.77 .72 do Zinc hydroxide..... Colloidal hydrated Ethanol ..do .64 .64

- flum nsilica e.

.48 ..5l 4 Calcium Bentonite. L Ethanol:Acetone- .72 .67 Laws. =13 ..do. ..Qdo do .53 .49 5 ..do. Barium carbonate kaoli Styrene-buta- .60 .64

- tdienelatex. do ..do ..do ..do .43 .48 6 do Aluminum Zeolite .FEthanol Ethyl cellulose .59 .61

. hydroxide. B ..do "30:... ..do ..do .47 .53 7 A ..do.. Magnesium Talc Ethyl acetate ..do .59 .59

hydroxide. B ..do ..do....' ..do ..do .46 .51 8 A ..do Zinc oxide Colloidal hy- Ethanol ..do .79 .76

- drated aluminum silicate.

tive Test Result 3 was carried out.

The results are shown in Table 4.

TABLE 4 Fresh density Example A Fresh density in the case of and I in the case of B-dibenzylamino- Wmpflrmwc Polymer i Metallic compound Inorganic pigment Solve nt Binder crystal violet 7-diethylamino No. example B lactone "fluorane 10 A P-2 Zinc carbonate..... Zinc silicate Ethanol Ethyl cellulose 0.97 0.83 ..do ..do ..do... ..do .83 .78

ii A ..do Zinc oxide Organic ben- Ethanol ..do .95 .82

tonne. B ..do ..do .1: ..do ..do .70 .65 12 A ..do Zinc hydrozide..... Bentonite Benzene Styrene-buta- .70 .76

d itelatex- B ..do ..do ..do ..do... .52 .58 13 A ..do Calcium Colloidal hydrated Ethyl cellu- ..do .71 .72

carbonate. aluminum silic t 195?- B ..do ..do .i ..do ..do .56 .60 14 A ..do Basic lead .70 .73

hyd at .....do ..do .55 .58 l5 Basic lead .73 .72

aluminum B ..do ..do ..do ..do .6l .65

As shown in Tables 3 and 4, the color developer sheet of the present invention, that is, a color developer sheet having combined a polymer, a metallic compound and an inorganic pigment, is more excellent in comparison with that having combined a polymer and a metallic compound.

And also, the color images formed on the color developer sheet of the present invention did not disappear even in the case of wetting with water.

Example 5 138 parts of salicylic acid and 325 parts of 37 percent Table 5 Varnish Polymer (P-l) Metallic compound Pigment No. (parts) (parts) (parts) (parts) I 67 8 25 (zinc oxide) 2 70 i 20 (calcium oxide) 3 72 8 15 (aluminum (organic hydroxide) bentonite) 154 parts of 2,6-dihydroxybenzoic acid and 325 parts of 37 percent formaldehyde were polymerized by adding 250 parts of 12 N sulfuric acid thereto under heating at 95-97 C for 1 hour to obtain a polymer (P-2).

A solution (hereinafter referred to as Varnish B) was prepared by mixing parts of nitrocellulose, 30 parts of butyl acetate, 40 parts of ethyl alcohol and parts of methyl cellulosolve. To the solution, the polymer (P-2) and the additives shown in Table 6 were added by means of a ball mill to provide a color developer ink.

TABLE 6 Varnish Polymer B (P-2) Metallic compound Pigment No. (parts) (parts) (parts) (parts) 4 65 I0 (zinc carbonate) 5 66 l0 19 (basic aluminum 5 (kaolinacetate) ite) diluted with a solvent shown in the following Table 7 so as to be a viscosity of about centipoise, and then was applied to a paper in a dry thickness of 2 g/m by flexo or'gravure printing method. The thus-obtained color developer sheets were placed on a color former sheet (crystal violet lactone or 3-dibenzylamino-7- diethylamino fluorane) and pressurized under 600 kg/m to form color images.

After being allowed to stand in the dark for one hour, spectral absorption curves of the color images were measured at wavelengths of 400700 mg, and a density at the maximum absorption was defined as a color developing ability. The results are shown in the following Table 7.

TABLE 7 Density crystal 3-benzylamino- Solvent for Printing violet 7-diethylamino No. dilution method lactone fluorane l Ethyl Flexo 0.80 0.75

alcohol 2 Ethyl Flexo 0.72 0.70

alcohol 3 Ethyl Flexo 0.59 0.67

alcohol 4 lsopropyl Flexo 0.98 0.92

alcohol 5 isopropyl Flexo 0.73 0.78

alcohol As is apparent from Table 7 above, the color developer ink of the invention gives a more excellent color developing ability even in case of thin coatings (2 glm Furthermore, even if the color images were wetted with water, the color density was not lowered.

What is claimed is: i

l. A recording sheet comprising, in combination with a color former which comprises a colorless dye-forming organic compound, a support having coated thereon a layer of a color developer containing a combination of (i) a polymer of (a) an aromatic carboxylic acid or (b) its anhydride with an aldehyde or acetylene, said polymer having at least one hydroxyl group, and (ii) a metallic compound selected from the group consisting of a metal oxide, a metal hydroxide and a metal carbonate, said color developer being capable of forming a distinct color when contacted with said color former, the amount of said polymer being at least one part by weight based on l00parts by weight of said metallic aqan.

2. The recording sheet of claim 1 wherein said polymer is salicylic acid-aldehyde polymer, ph'ydroxybenzoic acid-aldehyde polymer, 2,6- dihydroxybenzoic acid-aldehyde polymer or salicylic acid-acetylene polymer.

3. A recording sheet of claim 1 wherein said metal is selected from the group consisting of metals of groups Ila, lib, Illa and IVa of the Periodic Table.

4. The recording sheet of claim 1 wherein said color developer further contains a pigment.

5. The recording sheet of claim 1 wherein said metallic compound is selected from the group consisting of zinc oxide, cadmium oxide, magnesium oxide, zinc hydroxide, magnesium hydroxide, calcium hydroxide,

zinc carbonate, calcium carbonate and magnesium carbonate and wherein said metallic compound is in the 8. The recording sheet of claim 7 wherein the amount of said pigment is from 10 to 500 parts by weight per 100 parts by weight of said polymer.

9. The recording sheet of claim 1 wherein said color developer layer further consists essentially of a binder therefor.

10. The recording sheet of claim 1 wherein said color developer layer is coated onto said support in an amount of greater than 0.1 gram per square meter.

1 l. The recording sheet of claim 11 wherein said color developer layer is coated onto said support in an amount of from 0.5 to 10 grams per square meter.

12. The recording sheet of claim 1 further consisting essentially of an alkali metal salt of an organic acid or an alkali compound in an amount of from 0.01 to 1 part by weight per 1 part by weight of said polymer.

13. The recording sheet of claim 1 wherein said color former is coated on the same side of said support as said layer of said color developer.

. 14. The recording sheet of claim 1 wherein said color former is coated on the opposite side of said support I from said layer of said color developer.

of said color developer. 

2. The recording sheet of claim 1 wherein said polymer is salicylic acid-aldehyde polymer, p-hydroxybenzoic acid-aldehyde polymer, 2,6-dihydroxybenzoic acid-aldehyde polymer or salicylic acid-acetylene polymer.
 3. A recording sheet of claim 1 wherein said metal is selected from the group consisting of metals of groups IIa, IIb, IIIa and IVa of the Periodic Table.
 4. The recording sheet of claim 1 wherein said color developer further contains a pigment.
 5. The recording sheet of claim 1 wherein said metallic compound is selected from the group consisting of zinc oxide, cadmium oxide, magnesium oxide, zinc hydroxide, magnesium hydroxide, calcium hydroxide, zinc carbonate, calcium carbonate and magnesium carbonate and wherein said metallic compound is in the form of fine particles thereof having a size which will pass a sieve of more than 325 mesh.
 6. The recording sheet of claim 1, wherein the amount of said polymer is from 10 to 30 parts by weight based on 100 parts by weight of said metallic compound.
 7. The recording sheet of claim 6 wherein said color developer further consists essentially of at least one part by weight, based on 100 parts by weight of said polymer, of a pigment.
 8. The recording sheet of claim 7 wherein the amount of said pigment is from 10 to 500 parts by weight per 100 parts by weight of said polymer.
 9. The recording sheet of claim 1 wherein said color developer layer further consists essentially of a binder therefor.
 10. The recording sheet of claim 1 wherein said color developer layer is coated onto said support in an amount of greater than 0.1 gram per square meter.
 11. The recording sheet of claim 1 wherein said color developer layer is coated onto said support in an amount of from 0.5 to 10 grams per square meter.
 12. The recording sheet of claim 1 further consisting essentially of an alkali metal salt of an organic acid or an alkali compound in an amount of from 0.01 to 1 part by weight per 1 part by weight of said polymer.
 13. The recording sheet of claim 1 wherein said color former is coated on the same side of said support as said layer of said color developer.
 14. The recording sheet of claim 1 wherein said color former is coated on the opposite side of said support from said layer of said color developer.
 15. The recording sheet of claim 1 wherein said color former is coated onto a second support which is separate from said support having coated thereon said layer of said color developer. 